|Publication number||US7038633 B2|
|Application number||US 10/488,666|
|Publication date||May 2, 2006|
|Filing date||Aug 26, 2002|
|Priority date||Sep 4, 2001|
|Also published as||DE60227083D1, EP1428043A1, EP1428043B1, US20050012658, WO2003021287A1|
|Publication number||10488666, 488666, PCT/2002/1522, PCT/SE/2/001522, PCT/SE/2/01522, PCT/SE/2002/001522, PCT/SE/2002/01522, PCT/SE2/001522, PCT/SE2/01522, PCT/SE2001522, PCT/SE2002/001522, PCT/SE2002/01522, PCT/SE2002001522, PCT/SE200201522, PCT/SE201522, US 7038633 B2, US 7038633B2, US-B2-7038633, US7038633 B2, US7038633B2|
|Inventors||Mats Gunnar Hakan Eriksson|
|Original Assignee||Telefonaktiebolaget Lm Ericsson (Publ)|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (6), Classifications (10), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a 371 of PCT/SE02/01522 filed Aug. 26, 2002.
The present invention generally relates to an antenna system network architecture and a method for detecting and correcting drift in such a network. More particularly the present invention relates to an active phased array antenna system and a calibration method for such a system.
In some antenna systems with steerable beams or directional capabilities, such as active phased array radar antennas or active telecommunication base-station antennas, numerous antenna elements are arranged equidistantly in a plane whereby each element is adapted to emit and receive microwave signals.
In those systems, typically a microwave exciter and receive unit is provided for generating and receiving a signal. The exciter and receive unit is connected to a branch like transmission network, through which signals are emitted and received. The transmission network connects to respective transmit and receive modules, TRM, comprising electrically controllable phase shifters and amplifier stages through which the amplitude and phase delay of signals can be controlled. The transmit and receive modules are connected to the antenna elements. Typically, dipole elements may be used as antenna elements.
When signals are provided simultaneously to the plurality of elements, a plane wavefront parallel to the plane of the array is generated because of the in-phase interference of individual signals. When the phases of signals are incremented for each antenna element with regard to an adjacent element, a wavefront is propagating at a non-parallel angle with regard to the plane of the elements, which angle is dependent on the incremental phase delay. The elements may also be arranged at non-equidistant intervals, but then the individual delays are correspondingly controlled to provide a plane wavefront. By arranging a plurality of elements on a plane and controlling the emission with regard to two directions, the resulting direction of the emitted beam and the sensitivity of the received signal may be controlled in three-dimensional space.
One disadvantage associated with known active antenna systems is the amount of hardware required. A phased array antenna may for instance have several thousand individually controllable antenna elements.
Moreover, it is important that all individual transmission paths are of the same or of known length to accomplish the desired beam-steering control over the desired bandwidth.
An important characteristic of an antenna system with high sensitivity is the directional properties as expressed by the level of the side-lobes compared to the level of the main lobe.
For instance for airborne radar systems, such as Airborne Early Warning (AEW) systems, the side-lobes must be so well attenuated that unwanted ground and sea clutter can be efficiently suppressed. Low sidelobes are also required in order to suppress signals from other emitters in the neighbourhood such as signals from active hostile jamming. The low sidelobe level specification necessitates a tight control of the amplitude and phase of each transmit/receive module, TRM. When transmitting, the amplitudes of all TRMs have identical settings, whereas amplitude tapering is applied in receive mode. In air-cooled systems, the phase and amplitude control must cope with the large temperature variations that may prevail. This particularly applies to air-borne radar systems. For instance the feed and receive network may be subject to thermal expansion/contraction, which alters the phase of individual signals. One example of AEW system has been shown in U.S. Pat. No. 4,779,097.
Generally, antenna systems are complex systems with many components, which require accurate control.
In a distributed transmission system, utilising microwave wave-guides, the transmit and receive modules account for a majority of the errors that are introduced. Careful design of these parts with respect to long-term stability of performance, supply voltages, internal heating and ambient temperature is necessary but often not sufficient. Therefore, a need has arisen as to be able to calibrate antenna systems during operation.
The 1-k antenna elements may be evenly dispersed over a rectangular plane in a pattern of rows and columns.
The exciter/receiver unit, ERU, has a data bus XD, over which the exciter receiver unit controls the individual transmit and receive modules TRM for obtaining the desired directional capabilities.
Each respective T/R module has a feed AF that leads to an antenna element. The calibration network C constitutes a branch like structure with equally long distance to each respective coupler Q1–Qk. Calibration signals are sent through a port X, of the ERU, returning through a selected transceive and receive module TRM and returning through the first feed network R back to the ERU over the transmission network, R. The phase and amplitude of the signal is compared to a fixed reference for a given path. This procedure is completed for all transceive and receive modules, TRM.
Prior art document U.S. Pat. No. 5,412,414 shows a similar phased array radar system providing in-operation calibration. The radar system comprises an exciter, a receiver, a transmit/receive transmission network, T/R modules and dipole elements. Respective directional calibration couplers are provided adjacent the dipole elements for transferring signals through these to/from a calibration network which is different from the transmit/receive network. By issuing transmitting calibration signals from the exciter and leading signals through the transmit/receive transmission network and through individual T/R modules to couplers adjacent selected dipole elements, and return through the calibration network, variations in the transmit/receive network and associated components can be analysed. Likewise, by issuing receiving calibration signals from the exciter and leading signals through he calibration network to couplers adjacent selected dipole elements, and return through T/R module and the transmit/receive network, variations in the transmit/receive network and associated components can be analysed. One drawback with the above system is that an initial calibration, using external measurement equipment, seems to be required before in-operation calibrations can be carried out.
U.S. Pat. No. 5,874,915 shows an AEW phased array system having a plurality of selector switches for coupling a respective low noise receive amplifier or transmit amplifier to one of three antenna elements in a respective column of the antenna array.
It is a first object of the present invention to set forth an antenna system, which allows verification of error free operation while the system operates or in direct connection with operation.
It is a second object of the invention to set forth an antenna system in which calibration nets or branches through a calibration net can be compared.
It is a third object of the invention to achieve a calibration network structure that can be cost effectively produced.
It is a fourth object of the invention to enable the drifts in panels caused by e. g. hot or cool spots to be detected.
It is a fifth object to accomplish extensive calibration possibilities in an antenna system of less extensive complexity with a reduced number of components.
It is a further object to detect drift in a calibration net for an antenna system.
It is another object to establish which calibration net is drifting.
It is a still further object to calibrate a calibration network.
Further advantages will appear from the following detailed description of the invention.
A plurality of couplers Q111–Qnhv is provided, such that for each antenna element D there is preferably arranged a coupler Q adjacent an antenna element. As appears from the figure, for instance coupler Q211 is arranged next to the antenna element D211. Preferably, the respective coupler is arranged close to the antenna element and adjacent a segment of the antenna feed AF2 for that particular element. A plurality of calibration networks are provided, C1–Cj, and each calibration network couples to a subset of the couplers Q111–Qnhv. Each calibration net branches off from a port, X1–Xj, on the calibration unit, CU, to various couplers belonging to a subset of antennas to be served. Hence, each calibration network is separate and connected to a designated port on the calibration unit, CU. The separate calibration networks are not connected to one another. By way of example, if a signal is issued on port X1 of CU, the signal is lead to calibration network C1 and to couplers Q111, Q112, Qn12, Q1hv and coupled to respective antenna feeds to corresponding ports on the various T/R modules. Likewise, a signal on port P1 of TRM1 will be transferred to coupler Q111, calibration network C1 and port X1 of calibration unit CU.
Advantageously, the couplers are formed as strips arranged at a point adjacent a given antenna feed and close to the antenna element in question. However; the couplers may also be electrically connected over a suitable impedance or waveguide to the antenna element. The coupler may be realised in stripline technology as is well known in the art.
The calibration nets and the feed and receive net are advantageously formed as tree structures with a number of branches. However, other grid structures and non-branched structures are also possible.
The T/R module comprises a phase shift and attenuation module, PSAM, a power amplifier module, PAM, a logic bias board, LBB, a low noise amplifier, LNA, and a switch module, SM. The logic bias board, LBB, controls the individual functions of the above mentioned modules, such that the phase and amplitude of both transmitted and received signals are controlled according to a desired directivity pattern in a conventional fashion. The logic bias board, LBB, moreover controls the switch module, SM, to select radio frequency signals to or from the XR port of the ERU to one of the various ports P1 to Pn in a manner, which shall be explained later.
In transmit mode, the antenna system controls the beam forming in a conventional way. A microwave signal is emitted on the transmission network R. This signal is received at the various T/R modules TRM substantially synchronously. In each T/R module (1-k) for each connection (1-n), the input signal is processed individually, such that respective signals to respective antenna elements (1-h·v) have the required phase and amplitude properties for obtaining the desired beam form. For this purpose, corresponding signals are sent over port XD to logic bias board, LBB, which controls the phase shift and attenuation module, PSAM, and the power amplifier module, PAM.
In receive mode, the antenna system accomplishes the required focussing in a conventional way by controlling the phase and amplitude of incoming signals from low noise amplifier LNA in each respective T/R module. For this purpose, control signals are issued from the logic bias board LBB to control the phase and attenuation module, PSAM.
The antenna elements of a given panel number are connected to a given port number of every transmit and receive unit. According to the invention, each panel and corresponding sector is served one at a time, by operating the switches SM in each TRM module synchronously and selecting a given port number.
Hence, each T/R module serves all three panels through ports P1–P3 (n=3) in a sequential or time multiplexed manner, whereby during operation each switch module SM of a particular T/R module serves a particular port number. Thereby, the antenna is beaming into each sector according to the desired beam pattern.
In base station applications, the sectors may be illuminated sequentially with a fixed period and in a fixed order. For other applications such as radar, the panels may be served so as to give preference to a desired direction or with a certain weight with regard to a certain sector, that is, serving a particular sector longer than average according to the choice of an operator.
It appears, comparing the above antenna with a full permanent coverage, that the number of T/R modules, the feed and receive network complexity, and the exciter receiver unit processing power requirement are cut by two thirds.
In the above example, three panels are utilised. However, the inventive concept may just as well be applied to two or four panels or a larger number of panels. If only two panels are used, the antenna panels can be mounted back to back, which provides for reduced dimensions of the calibration and antenna feed networks.
Advantageous embodiments combining aspects of the first and second embodiments shall now be described.
According to a second embodiment for arranging the calibration nets, having the basic outline as shown in
As mentioned above, the calibration nets are advantageously formed as separate nets, which are isolated from one another, each calibration net being connected to a respective port X1, X2, X3 . . . on the main unit MU. However, some part of the calibration net could also be common and various calibration nets could branch off from a switch, such that individual branches of the calibration nets could be disconnected from one another. Various calibration nets could also branch off from a node. Generally, it is desired that individual branches can be exposed to calibration signals such that alternative paths through the calibration net or alternative calibration nets can be compared.
A third embodiment for arranging the calibration nets having the basic outline as shown in
For the above three embodiments, it should be understood that in most practical circumstances the number of antenna elements would be much larger, for instance thousands of antenna elements per panel.
A first calibration routine of the invention shall now be explained with reference to
The attenuation and phase delay CS111R of the signal is measured. This value is compared with fixed values CS111Rfix derived for instance from a reference measurement using additional calibration apparatus. The result of the comparison, Δ111, corresponds to the attenuation and phase delay differences at a given time in relation to the reference values in T/R module 1, antenna feed AF111 and the corresponding branch in receive and transmit network R.
The set of values Δ111 is stored for being able to compensate the amplitude and phase of signals from or to the exciter and receiver module for accomplishing the directional steering capabilities of the antenna system. This corresponds to the conventional calibration of the steerable antenna system.
Subsequently, a new calibration signal is emitted on port X2, as shown in
CS211R is compared with a fixed value CS211Rfix. The result, Δ211, as above, corresponds to the attenuation and phase delay in T/R module 1, the antenna feed AF2 and the corresponding branch in receive and transmit network R.
Besides errors in the port switch (1-n) in TRM1 together with the cabling of AF1 and AF2, the results from the two measurements Δ111 and Δ211 should be of the same size. If not, a drift in one (or both) of the calibration nets 1 and 2 has been detected (or a drift in AF1 or AF2).
Hence, it can be established whether the system is functioning correctly or not.
Subsequently, a new calibration signal is emitted on port X2 and transferred on net C2, as shown in
CS2hvR is compared with a fixed value CS2hVRfix. The result Δhv, as above, corresponds to the amplification and phase delay in T/R module TRMk, antenna feed AF2hv and the corresponding branch in receive and transmit network R.
This routine is repeated for all antenna elements and all calibration nets.
Now we have a number of m times n measurements that should agree. As an example, where n=3 and a situation is occurring where two measurements agree, the third measurement and corresponding calibration net is most probably drifting.
Hence, apart from establishing whether the system is functioning correctly or not, in the latter case K can moreover be established in which calibration net there is a drift. Moreover, the drifting calibration net can be calibrated by appropriate adjustment of the given amplitude and phase settings for the individual T/R modules, all controlled over the databus XD of the excite and receive unit, ERU.
Hence, not only are the TIM modules and antenna feed examined with regard to drift, also the calibration nets are subject to an examination for drift. Thereby, the erroneous calibration net can be identified and corresponding compensation can be carried out. This procedure can be done virtually while the system operates or causing only a short interruption.
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|U.S. Classification||343/853, 342/375, 343/876, 343/754|
|International Classification||H01Q3/26, H01Q21/24, G01S7/40|
|Cooperative Classification||H01Q3/267, G01S7/4017|
|Sep 17, 2004||AS||Assignment|
Owner name: TELEFONAKTIEBOLAGET LM ERICSSON (PUBL), SWEDEN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ERICSSON, MATS GUNNAR HAKAN;REEL/FRAME:015146/0746
Effective date: 20040902
|Mar 3, 2005||AS||Assignment|
Owner name: TELEFONAKTIEBOLAGET LM ERICSSON (PUBL), SWEDEN
Free format text: TO CORRECT NAME OF CONVEYING PARTY ON REEL/FRAME 015146/0746;ASSIGNOR:ERIKSSON, MATS GUNNAR HAKAN;REEL/FRAME:015825/0466
Effective date: 20040902
|Dec 11, 2007||CC||Certificate of correction|
|Nov 2, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Nov 4, 2013||FPAY||Fee payment|
Year of fee payment: 8